Hydrodynamics and mass transfer in three-phase magnetic fluidized beds

The mass transfer coefficient. liquid axial dispersion and gas holdup have been measured for a gas-liquid-solid magnetic fluidized bed (MFB) as a function of superficial gas velocity, superficial liquid velocity and magnetic field intensity. This study analyzed the volumetric gas-to-liquid mass transfer coefficient k(La) to quantify mass transfer in three-phase MFBs. The solid phase consisted of nickel powder with mean particle diameter of 194 mum, and the liquid and gas phases were water and air, respectively. An axial magnetic field was supplied by an external solenoid with direct current, the magnetic field being approximately uniform with a maximum relative variation of 2% across the bed. The volumetric gas-to-liquid mass transfer coefficient k(La) was determined from measurements of the steady-state oxygen profile across the bed. Experimental results showed that the mass transfer rate and average gas holdup in the MFB were higher compared to those of conventional fluidized beds. A 70% increase in mass transfer coefficient was observed at high magnetic field intensities. Average gas holdup increased by as much as 25% with increasing magnetic field intensity. The efficiency of mass transfer rare is nearly the same as a solid-free bubble column. The experimental results were compared to the published results of conventional fluidized beds. (C) 2001 Elsevier Science B.V. All rights reserved.